The present invention generally relates to the continuous separation of solid particles, such as soot, from a fluid, such as oil, by use of a centrifuge. More specifically, but not exclusively, the present invention relates to a centrifuge that includes two separate fluid paths in which one of the fluid paths travels through a particulate collection zone of the centrifuge and the other path bypasses the particulate collection zone to directly drive the centrifuge through jet nozzles.
Diesel engines are designed with relatively sophisticated air and fuel filters (cleaners) in an effort to keep dirt and debris out of the engine. Even with these air and fuel cleaners, dirt and debris, including engine-generated wear debris will find a way into the lubricating oil of the engine. The result is wear on critical engine components and if this condition is left unsolved or not remedied, engine failure. For this reason, many engines are designed with full flow oil filters that continually clean the oil as it circulates between the lubricant sump and engine parts.
There are a number of design constraints and considerations for such full flow filters and typically these constraints mean that such filters can only remove those dirt particles that are in the range of 10 microns or larger. While removal of particles of this size may prevent a catastrophic failure, harmful wear will still be caused by smaller particles of dirt that get into and remain in the oil. In order to try to address the concern over small particles, designers have gone to bypass filtering systems which filter a predefined percentage of the total oil flow. The combination of a full flow filter in conjunction with a bypass filter reduces engine wear to an acceptable level, but not to the desired level. Since bypass filters may be able to trap particles less than approximately 10 microns, the combination of a full flow filter and bypass filter offers substantial improvement over the use of only a full flow filter.
In high performance soot centrifuge (HPSC) designs, such as the one disclosed in U.S. Pat. No. 6,019,717 that was issued on Feb. 1, 2000 to Herman, which is incorporated by reference in its entirety, the inventors of the present invention have found that the collection rate of super-fine particulates, such as soot, increases by decreasing the flow rate passing through the rotor of the centrifuge. Traditional centrifuge theory predicts that reducing the flow rate in the rotor by half will result in a doubling of the single-pass collection efficiency of the centrifuge. Although the collection efficiency improves, since the flow rate is cut in half, the collection rate of particulates should remain unchanged. Graph 30, which is show in FIG. 1, graphically illustrates this predicted effect for super-fine particles, such as soot. As shown, graph 30 includes a flow rate axis 32 and a collection rate axis 33. Prediction line 35 in graph 30 illustrates the prediction that flow rate through the centrifuge has no effect on the collection rate. However, the inventors of the present invention have discovered that this theory does not appear to hold up in super-fine particulate regime where collection efficiencies are typically well under 0.5% on a single pass basis. As shown with actual line 36, the collection rate of the super-fine particles increases as the flow rate is decreased. It is theorized that the collection rate is improved at the lower flow rate though reduced re-entrainment of particulates in the fluid. The reduced flow rate diminishes fluid eddies and flow passing in close proximity to the collected particles (sludge) in the sludge collection zone of the centrifuge, which in turn reduces the amount of re-entrainment of the collected particles. The HPSC design allows for the freedom to reduce the rotor xe2x80x9cthrough flowxe2x80x9d rate without penalizing rotor speed. In the HPSC design, the fluid flow driving upon an external Pelton turbine is independent from the rotor flow rate so that the flow rates can be independently adjusted.
Unfortunately, in the lower cost and widely used hero-turbine centrifuge designs, (such as the ones disclosed in U.S. Pat. No. 5,795,477 that was issued on Aug. 18, 1998 to Herman et al. which is incorporated by reference in its entirety) simply reducing the rotor through flow to take advantage of this effect, does not work. In the hero-type centrifuges, a single flow path is used for both separation of particulates from the fluid and driving the centrifuge. Reducing the flow rate in the rotor reduces rotor speed because the rotation driving power is proportional to the rotor flow rate. One type of solution, such as disclosed in U.S. Pat. Nos. 3,784,092 and 5,906,733, is to provide two separate fluid sources, one for driving the centrifuge and the other for separation. However, using the two separate fluid sources in these designs increases the complexity and expense of the centrifuge. Furthermore, retrofitting such types of centrifuges to pre-existing systems is costly because additional piping needs to be installed.
While important strides have been made in this field, there still is room for improvement in the areas of particulate separation.
A centrifuge according to one embodiment of the present invention includes a rotor shell that defines an inner cavity. The rotor shell has a jet orifice defined therein that discharges fluid in order to rotate the rotor shell. A divider is provided in the inner cavity, which divides the inner cavity into a drive cavity and a separation cavity for collecting particulate matter from the fluid. The divider defines at least in part a divider passage between the separation cavity and the drive cavity, and the jet orifice open into the drive cavity. A tube extends within the inner cavity, and the tube has a fluid passage constructed and arranged to supply the fluid. The tube defines a separation opening at the separation cavity and a bypass opening at the drive cavity. The tube is constructed and arranged to deliver the fluid to the drive cavity through both a bypass flow path and a separation flow path. The bypass flow path includes the bypass opening. The separation flow path includes the separation opening, the separation cavity and the divider passage. The drive cavity is constructed and arranged to discharge the fluid received from both the bypass flow path and the separation flow path out the jet orifice.
A centrifuge according to another embodiment includes a shaft having a single fluid passage defined therein to supply fluid to the centrifuge. The shaft has one or more fluid ports defined therein that are in fluid communication with the fluid passage. A tube is provided around the shaft, and both the tube and the shaft define a tube passage that is in fluid communication with the fluid port. A rotor shell defines an inner cavity in which the tube is positioned. A divider plate is provided around the tube, and the divider plate divides the inner cavity into a drive cavity and a separation cavity. The divider plate defines a divider passage between the separation cavity and the drive cavity. The tube defines a separation opening in order to communicate the fluid between the tube passage and the separation cavity. The tube defines a bypass opening to communicate the fluid between the tube passage and the drive cavity. A baffle is positioned in the tube passage between the fluid ports and the separation opening. The baffle divides the tube passage into a separation portion and a bypass portion. The baffle is constructed and arranged to separate a separation flow path of the fluid from a bypass flow path of the fluid. The separation flow path includes the separation portion of the tube passage, the separation opening, the separation cavity, the divider passage, and the drive cavity. The bypass flow path includes the bypass portion of the tube passage, the bypass opening, and the drive cavity. At the drive cavity, the rotor shell has defined therein at least one jet nozzle, which is constructed and arranged to rotate the rotor shell by discharging from the drive cavity the fluid from the separation flow path and the bypass flow path.
A centrifuge according to another embodiment includes a rotor shaft that has a single fluid supply passage that supplies fluid to the centrifuge. The shaft defines one or more separation ports that are in fluid communication with the fluid supply passage. The shaft defines one or more bypass ports that are in fluid communication with the fluid supply passage. A tube is provided around the shaft, and the tube along with the shaft defines a tube passage. A baffle is positioned in the tube passage between the bypass ports and the separation ports. The baffle divides the tube passage into a bypass portion that is in fluid communication with the bypass port and a separation portion that is in fluid communication with the separation port. The baffle is constructed and arranged to minimize fluid leakage between the bypass portion and the separation portion. A rotor shell defines an inner cavity in which the tube is positioned. A divider plate is provided around the tube, and the divider plate divides the inner cavity into a drive cavity and a separation cavity. The divider plate defines a divider passage between the separation cavity and the drive cavity. The tube defines a separation opening between the separation portion of the tube passage and the separation cavity. The tube defines a bypass opening between the bypass portion of the tube passage and the drive cavity. The rotor shell defines a jet nozzle at the drive cavity, and the jet nozzle is constructed and arranged to rotate the rotor shell by discharging fluid from the drive cavity.